This invention relates to methods of forming titanium comprising layers, and to methods of forming conductive silicide contacts.
In the processing of integrated circuits, electrical contact is typically made to isolated active device regions formed within a wafer substrate typically comprising monocrystalline silicon. The active regions are typically connected by highly electrically conductive paths or lines which are fabricated above an insulating material formed over the substrate surface. Further, electrical contact is also typically made to other conductive regions received outwardly of the bulk wafer, such as to conductive lines, contact plugs and other devices. To provide electrical connection between two conductive regions, an opening in an insulating layer is typically etched to the desired regions to enable subsequently formed conductive films to connect with such regions. Where the desired region comprises silicon, conductance can be greatly enhanced by forming a conductive metal silicide interface with the silicon region.
Silicide layers might be formed in a number of manners. For example, a metal layer such as titanium might be deposited onto a silicon comprising substrate, and subsequently subjected to a high temperature anneal sufficient to react the titanium with the silicon to form titanium silicide. Alternately, the deposition conditions for depositing an otherwise elemental titanium layer might be sufficient to cause reaction during the deposition between the titanium and underlying silicon to form the silicide. Even further alternately and by way of example only, a titanium silicide might be directly chemical vapor deposited onto a substrate.
Regardless, TiCl4 is one example prior art preferred precursor gas for chemical vapor depositing titanium, titanium silicide or a mixture thereof, with or without plasma. Chlorine atoms from the TiCl4 can undesirably be incorporated into the elemental titanium and/or titanium silicide layer being formed over a substrate. Further, chemical vapor deposited titanium and titanium silicide films are susceptible to incorporating oxygen from room ambient. This can potentially form occluding insulative oxide layers at worse, or result in interstitial oxygen atom incorporation which reduces conductance at best. Further, chlorine incorporation can lead to poor addition of the film to substrates as well as excessive oxidation when exposed to oxygen or moisture in the ambient.
One prior art technique for preventing oxygen incorporation is to passivate the deposited titanium and/or titanium silicide layer with a nitrogen atmosphere, such as using plasma or with higher pressure nitrogen atmosphere exposure. Such can result in forming an outer region of such layers which is higher in nitrogen concentration than lower regions, perhaps forming TiN which is a conductive barrier layer substantially impermeable to oxygen or subsequent oxidation at typical ambient conditions. However passivation with a nitrogen containing atmosphere undesirably has the adverse effect of increasing ultimate chlorine content of the titanium and/or titanium silicide film, as well as increasing the tensile stress of the film. Such is believed to be due to formation of a barrier portion at the top of the layer which prevents conventional inherent driving of chlorine from such layer in later processing steps. Further, the resultant higher chlorine concentration inherently leads to increased tensile stress in the film. These adverse effects are deleterious to film performance in terms of adhesion and peeling and may also have issues with long term reliability of the deposited film.
While the invention was principally motivated and resulted from achieving solutions to the above-identified problems, the invention is not so limited, with the scope being defined by the accompanying claims as literally worded and interpreted in accordance with the doctrine of equivalence.
The invention comprises methods of forming titanium comprising layers, and methods of forming conductive silicide contacts. In one implementation, a method of forming a titanium comprising layer includes chemical vapor depositing a layer a majority of which comprises elemental titanium, titanium silicide or a mixture thereof over a substrate using a precursor gas chemistry comprising titanium and chlorine. The layer comprises chlorine from the precursor gas chemistry. The layer is exposed to a hydrogen containing plasma effective to drive chlorine from the layer. In one implementation, a method of forming a conductive silicide contact includes forming an insulating material over a silicon comprising substrate. An opening is formed into the insulating material over a node location on the silicon comprising substrate to which electrical connection is desired. A layer is chemical vapor deposited over the substrate using a precursor gas chemistry comprising titanium and chlorine. The layer comprises chlorine from the precursor gas chemistry. The depositing forms a majority of the layer over the node location as titanium silicide, and a majority of the layer over the insulating material as elemental titanium. At least the majority titanium silicide portion of the layer is exposed to a hydrogen containing plasma effective to drive chlorine therefrom.